1. Field of the Invention
The present invention relates generally to a prosthetic foot. More particularly, the present invention relates to a prosthetic foot including a lap joint.
2. Background of the Invention
A useful prosthetic foot should simulate the operation and motion of an anatomical foot. An anatomical foot, including the ankle joint, is capable of motion around three perpendicular axes, as well as varying degrees of flexure. Specifically, the anatomical foot and ankle are capable of dorsiflexion, planiflexion, inversion, eversion, and transverse rotation. Dorsiflexion and planiflexion comprise the movement of the ball of the foot upward and downward, respectively, with respect to the heel. Inversion and eversion are the twisting of the foot around its longitudinal axis, resulting in outward and inward tilting of the ankles, respectively. Transverse rotation occurs when the foot rotates with respect to the longitudinal axis of the leg, such as occurs during left and right turns of the body.
In addition, it is desirable for a prosthetic foot to provide a spring effect during use (e.g., be capable of absorbing, storing, and releasing energy). At a minimum, the prosthesis should store enough energy to return itself to a relaxed, unflexed position when external forces are removed. Such a spring effect may be accomplished by the inclusion of energy-storing components such as coil springs. However, such energy-storing components may significantly increase the bulk and weight of the prosthesis, which may not be suitable for some amputees. For instance, additional weight and/or bulk may result in a prosthesis that is too heavy for some patients, such as geriatric patients, very young patients, or other patients who suffer some degree of muscular weakness.
Further, a useful prosthesis should provide a secure and reliable means for attaching the prosthesis to the amputee. Failure of the connection between the prosthesis and the amputee may result in injury to the amputee and may also necessitate expensive repairs or potentially a complete replacement of the prosthesis. It is also desirable to provide methods for connecting the prosthesis to the amputee that do not significantly inhibit the ability of the prosthetic foot to simulate the motion and flexion of the anatomical foot.
In some cases, the foot may be only partially amputated. In the US, the common reasons for partial (forefoot) amputations are: peripheral vascular disease, congenital deformities, trauma, infection, and tumors. There are at least two types of mid-foot amputation: Lisfranc amputation and Chopart amputation. In Lisfranc amputation, the fore-foot is amputated at the tarsometatarsal joints, with the lateral three metatarsals being separated from the cuboid and lateral cuneiform and the first and second metatarsals being separated from the medial and intermediate cuneiform respectively. In Chopart amputation, the fore-foot is removed at the midtarsal joint and a disarticulation occurs through the talonavicular and calcaneocubiod joints. In each case, the amputee retains the anile joint and its associated flexibility.
Although Chopart/Lisfranc amputees retain a significant portion of their anatomical ankle and heel, and thus may still partially rely on their anatomical ankle for motion, it is nonetheless desirable to provide a relatively lightweight and reliable prosthetic foot for Chopart/Lisfranc amputees that is capable of some of the motion, flexion, and cushion normally provided by the anatomical foot.
Some conventional prosthetic feet for Chopart/Lisfranc amputees employ a rigid, relatively flat prosthetic keel that is glued to the bottom of a socket worn by the amputee. In such conventional prostheses for Chopart/Lisfranc amputees, the resulting butt joint may be relatively weak since it relies solely upon the glue to hold it together. To increase the strength of such a butt joint, the surface area of the butt joint may be increased. For example, in some conventional foot prostheses for Chopart/Lisfranc amputees, the socket may be attached along up to 50% of the length of the keel. However, such a relatively large, rigid connection may detrimentally reduce the flexibility of the prosthetic foot as well as increase the bulk of the prosthetic foot, making it more difficult to wear and fit into a standard shoe or sneaker.
Thus, there remains a need to develop methods and apparatus for improved prostheses for Chopart/Lisfranc amputees which overcome some of the foregoing difficulties while providing more advantageous overall results.